Previously known safety masks are of design into which air is blown by an accumulator driven blower connected to the mask, or by a blower, close to the site of the mask, from which air is conducted to the mask along hoses.
The disadvantages of these masks have been, in the first case the weight of the transportable accumulator and its need to be charged which has to be done more often for the smaller the accumulator. In the other case, the disadvantage is that the user can move freely only within the outreach of the hoses. Further, the blowing has to be switched on and off by a separate switch.